Northamptonshire 219 (Zaib 90, Andersson 2-28) and 178 for 5 (Keogh 46*, Miller 42, Sales 40) lead Derbyshire 165 (Reece 50, Madsen 47, Chahal 5-45) by 232 runs
Indian leg-spinner Yuzvendra Chahal claimed five wickets as Northamptonshire ran through Derbyshire's batting line-up on a day dominated by spin at Wantage Road before Northamptonshire's batters put the hosts in the ascendancy.
Chahal, veteran of 152 white-ball internationals, finished with figures of five for 45, only his third career five-wicket haul, as Derbyshire lost their last six wickets for just 15 runs in 10.2 overs.
For most of the morning Chahal bowled in tandem with off-spinner Rob Keogh on a pitch offering plenty of turn and bounce with fielders stationed all around the bat. Keogh also took three wickets for 65 as Northamptonshire claimed a handy first inning lead of 54 on day two of this Vitality County Championship encounter.
Luis Reece had top scored for Derbyshire with 50 and while Wayne Masden (47) and Aneurin Donald (21) staged a fightback during a 51-run partnership, Chahal removed both batters in a lengthy spell which included a double wicket maiden.
In Northamptonshire's second innings, teenage Derbyshire quick Harry Moore took two early wickets for just six runs, before youngsters Gus Miller (42) and James Sales (40) mounted a stand of 76. Rob Keogh hit a well-paced unbeaten 46 as Northamptonshire closed on 178 for five, leading by 232 when heavy rain and bad light stopped play.
Earlier Ben Sanderson made the initial breakthrough for Northamptonshire, knocking back Brooke Guest's (28) off stump, while Reece's innings ended when he edged one from Keogh which spun away. Keogh struck again in his next over when David Lloyd was adjudged lbw as he attempted to sweep.
Masden refused to be bowled at, coming down the wicket to strike Keogh over midwicket, cutting and sweeping the spinners as he and Donald manoeuvred the ball into the gaps and kept the scoreboard ticking
Donald swept Chahal square for six when he tossed one up, but the bowler got his man when Donald swept a half-volley straight to Sales at square leg. Chahal almost had another wicket with his next ball but Sales, now at short leg, could not hold onto a sharp chance offered by Martin Andersson.
Masden was undone by one from Chahal that pitched middle and hit the top of off-stump, while Chappell, hero of the One Day Cup fixture here in July, fell two balls later when he chipped to Luke Procter who ran in to take a diving catch at mid-off. Keogh then removed Andersson thanks to an excellent sharp grab by Justin Broad at leg slip.
Chahal wrapped up the innings immediately after lunch, Alex Thomson top edging an attempted sweep, Prithvi Shaw running behind the stumps to take the catch. Chahal then bowled Jack Morley next ball to end the innings.
Debutant Moore had Shaw adjudged lbw in the second over of Northamptonshire's innings, while Procter edged him to Masden at second slip, the Derbyshire man's 250th first-class catch for the county.
Miller though started positively, driving Chappell through mid-on for four to get off the mark before Derbyshire turned to their own spin duo of Thomson and Morley who, while they created problems of their own, were inconsistent, failing to apply sustained pressure.
Miller cut Morley for four to take Northamptonshire's lead into three figures, Sales steering the spinner square for four and flicking him through midwicket for another. Miller duly drove Thomson through cover to bring up the 50 partnership.
Miller though became the latest batter to perish playing the sweep, trapped lbw by Thomson shortly before tea, while Sales departed to seam shortly after the break, given out caught behind off Andersson.
Saif Zaib and Keogh shared a stand of 41 for the fifth wicket to push the Northamptonshire lead towards 200. Zaib picked up where he had left off in his first innings 90, playing some crisp drives against Andersson and reverse sweeping the spinners, but he departed in a rush of blood, bowled as he danced down the track to Morley.
Keogh profited from the reverse sweep in particular, deploying the shot to collect three consecutive boundaries off Thomson. He struck eight fours in total and despite the light worsening during the evening session, he helped Northamptonshire towards a daunting lead.